Dynamically load and use native C libs from Clojure using JNA
clojure-jna is available from clojars. Just add this to your Leiningen
project.clj in the :dependencies section:
[net.n01se/clojure-jna "1.0.0"](require '[net.n01se.clojure-jna :as jna])
(jna/invoke Integer c/printf "My number: %d\n" 5)
; My number: 5
;=> 13The first argument to jna-invoke is the native function's return value. The
second is a symbol, in this case c/printf. The c part is the name of the
library, in this case libc. The printf part is of course the name of the
function to call. The rest are arguments to the native function.
That 13 is printfs return value -- I guess it's the number of bytes printed or
something? Anyway, feel free to ignore it just like all C programs do.
If you're going to be calling the same function a few times, you might find it convenient to be able to call it like a regular Clojure function. Use jna-fn for that:
(doc jna/to-fn)
; -------------------------
; net.n01se.clojure-jna/to-fn
; ([return-type function-symbol])
; Macro
; Return a Clojure function that wraps a native library function:
; (def c-printf (jna/to-fn Integer c/printf))
; (c-printf "My number: %d\n" 5)
(def c-printf (jna/to-fn Integer c/printf))
(c-printf "My number: %d\n" 5)
; My number: 5
;=> 13
(c-printf "My number: %d\n" 10)
; My number: 10
;=> 14If you're going to be calling a bunch of functions from the same native lib, you might like to use jna-ns to create a Clojure namespace full of Clojure functions that wrap the native functions:
(doc jna/to-ns)
; -------------------------
; net.n01se.clojure-jna/to-ns
; ([new-ns libname fnspecs])
; Macro
; Create a namespace full of Clojure functions that wrap functions from
; a native library:
; (jna/to-ns native-c c [Integer printf, Integer open, Integer close])
; (native-c/printf "one %s two\n" "hello")
(jna/to-ns native-c c [Integer printf, Integer open, Integer close])
;=> #<Namespace native-c>
(native-c/printf "one %s two\n" "hello")
; one hello two
;=> 14
(native-c/open "README")
;=> -1